Question

Find the indicated sum of the geometric series. ∑6k=1−3(2)k−1

Answer 1

$\displaystyle\sum_{k=1}^63\times2^{k-1}=3\frac{1-2^6}{1-2}=189$

Or, if that hyphen between the lower index and 3 is actually a negative sign, then the sum is -189.